Bacteria resistant to antibiotics pose a grave danger to hospital patients. Now researchers have identified a gene that appears to make some strains of antibiotic-resistant germs more likely to erupt into hospital epidemics. Studying the gene may yield clues about how best to contain these otherwise unstoppable microbes.
Bacteria known as enterococci usually live peacefully in the human digestive system. But for patients with weakened immune systems, these bacteria can cause dangerous infections of the urinary tract and heart. Enterococcus faecalis is responsible for 75% of enterococcus infections. Another species, Enterococcus faecium, is rapidly acquiring resistance to antibiotics, including the "last resort" drug vancomycin. Researchers had already identified a gene called esp that appeared to make E. faecalis more virulent, or more likely to cause serious infection, but no connection had been made between virulence and esp in E. faecium.
Curious, a team of scientists led by Rob Willems of the National Institute of Public Health and the Environment in Bilthoven, the Netherlands, looked for esp in vancomycin-resistant E. faecium, or VREF. They discovered the esp gene in 15 of 16 VREF strains that were responsible for hospital epidemics in the United States, United Kingdom, the Netherlands, and Australia. In contrast, they didn't find the gene in benign strains from hospitals or healthy subjects, the researchers report in the 17 March issue of The Lancet.
It's not clear how esp makes bacteria more virulent. The gene encodes a protein that resides on the surface of the cell, and that protein may give bacteria the ability to bind and colonize tissue other bacteria can't, says Michael Gilmore of the University of Oklahoma Health Sciences Center in Oklahoma City. In the meantime, Willems adds, hospitals could help isolate and contain potentially infective strains by screening patients for VREF harboring the esp gene.